The present disclosure relates to a load bearing assembly. Particularly, it relates to a fretting relief slot for the load bearing assembly, the relief slot defined between adjacent surfaces of an outer race and a lug body of a load bearing assembly.
Spherical bearings within a rod or lug body are typically used to bear loads, and can be used for example to bear high loads in aerospace applications. Such arrangements often experience high frequency vibrations and reversals of loads in both the axial and radial directions of the spherical bearing, and hence they suffer from fretting as a consequence. Fretting is a general physical phenomenon that can occur between closely fitted components—e.g. between the spherical bearing outer race and the lug body—when relative motion causes corrosion damage, for example at the asperities of the contacting surfaces. Importantly, fretting promotes the onset of metal fatigue and can generate minute cracks and micro-fractures in the contact surfaces between the lug body and the outer diameter of the spherical bearing. The propagation of these cracks as a consequence of the fretting can eventually cause the lug body to break, resulting in catastrophic failure of the load bearing assembly.
Some load assemblies include substances between the spherical bearing outer race and the lug body to prevent or delay the onset of fretting fatigue and to mitigate the risk of catastrophic failure. Typically dry lubricants are used, for example: silver, molybdenum, graphite paste, and/or zinc nickel. However, the effects of these lubricants are limited and can be inconsistent due to their process dependent applications.
As part of the assembly process of such load bearing assemblies, the spherical bearing outer race lip is swaged onto the lug body. However, the process of swaging the spherical bearing outer race lip on to the lug body can stress the lug body itself, causing physical damage and further contributing to the possibility of catastrophic failure of the load bearing assembly.
As a consequence of fretting, the assembly can also experience alignment issues, which then exacerbate fatigue of the assembly by concentrating forces in unexpected regions, which in turn exacerbates fretting, yet further contributing to the possibility of catastrophic failure of the load bearing assembly.